Positive displacement flowmeter are well known in the art. Specifically, such a device is used in various applications within widespread industries, including the petrochemical and natural gas industries. The general purpose of a flowmeter is to measure the quantity of a substance, typically a gas or a liquid, flowing through the meter such that the amount of the substance can be readily and accurately determined.
Typically, a substance flows through a conduit or line designed to move the substance from one point to another. Where applicable, the conduit is separated and a flowmeter is attached and, in many instances, the entire flow path of the substance is then diverted through the flowmeter. The movement of the substance through the flowmeter causes the meter contained within the flowmeter apparatus to measure and/or record the quantity of substance moving through the flowmeter.
Given the typical application of a flowmeter, accuracy, flow volume and energy efficiency are important. It is desirable for the flowmeter to be accurate and measure precisely the amount of substance moving through the meter. In industrial settings, it is also desirable for the flowmeter to be able to accommodate an increased flow rate to maximize production and/or operations without jeopardizing the integrity and/or accuracy of the flowmeter.
The flow rate of the substance impacts factors that contribute to the longevity of a flowmeter, specifically pressure drop, cyclical pressure drop fluctuation and vibration. Over time these factors can damage the flowmeter thus decreasing both the accuracy of the meter and its longevity. When a flowmeter is damaged or ceases to work properly, the flow of the substance either has to be stopped or diverted so that the flowmeter can be detached from the conduit segments and a new flowmeter attached. Such downtime can significantly disrupt industrial operations.
Pressure drop and vibration generally increase with flow rate. Therefore, the structural design of the flowmeter, in as much as the design contributes to the degree of pressure drop and vibration, imposes a maximum flow rate on a flow meter above which accuracy and longevity is compromised. At a certain level of pressure fluctuation or vibration intensity, mechanical stresses will distort or flex the shapes of the rotors and/or the housing enough to allow unmetered flow, i.e. slippage, between the rotors and/or between the rotor and the housing, and/or cause physical damage to the bearing and other meter components, all directly impacting the accuracy and longevity of the meter.
A number of sources contribute to the pressure drop and vibration of a flowmeter as currently available in the art. First, in general, a flow path that is straight is only impeded by the friction exerted by the walls of the conduit and can move fluidly. However, as angles or turns are introduced into the path, which is typical in such applications, extra work is required to overcome inertia and the substance is met with increased friction at such angles or turns requiring greater energy to drive the device. The degree to which the flow of the substance is impacted or influenced depends on the degree of the angle or turn. The greater the degree of the turn, the greater the resistance.
The same principle is applicable for the flowmeter and the flow of substance through the flowmeter. A flowmeter that creates, by virtue of its structure, more turns and angles of the flow path will have greater pressure drop compared to a flowmeter with less turns and angles, other factors being equal. It is therefore desirable to have a flowmeter that creates a smooth, fluid flow path that minimizes turns and angles.
The second factor is the blocking rotors which impact flow in two ways, namely by virtue of both placement and design. In existing art designs, the blocking rotor is placed between the inlet and outlet in such a manner that the blocking rotor itself obstructs the inlet and outlet ports. The location of the blocking rotor within the flow path obstructing the flow generates cyclical vibrations that are undesirable. Therefore, it is desirable to position the blocking rotor such that it minimizes interference with the flow path.
Positioning the blocking rotor more directly between the displacement rotors decreases the interference with the inlet and outlet flows by the blocking rotor, a common problem existing in the art. It is desirable to increase the displacement rotor hub radius to substantially the same size as the blocking rotor radius to uniformly align the blocking rotor between the displacement rotors, reducing and/or eliminating the extent to which the blocking rotor interferes with the flow path. In a given housing size, the larger displacement rotor hub means shorter displacement rotor blades. In prior art, displacement rotor blade length was maximized to make the flow path as wide as possible in a given housing size. However, it is desirable to back away from maximum displacement rotor blade length in favor of reduced blocking rotor interference in the flow path, less turbulence inside and outside of the blocking rotor and improved efficiency. This is a trade off not seen in the prior art. The displacement rotor blades in prior models by Kolb and Richards extend to nearly the center of the blocking rotor, where the preferred embodiment displacement rotor blades reach less than half way to the center of the blocking rotor center, thus generating less turbulence inside the blocking rotor.
Regarding the blocking rotor design, current blocking rotors in the art have multiple recesses or cavities. The use of multiple cavities requires the blocking rotor structure to have a web(s) or wall(s) between the cavities. During the rotation of the blocking rotors, the flow confronts these walls which generate turbulence and vibrations in the meter.
Blocking rotors known in the art teach away from having a single cavity blocking rotor, as discussed in more detail later. However, a single cavity blocking rotor reduces the turbulence and vibrations in the meter by eliminating the rotating interior web surface which reduces turbulence, and reduces the work required to rotate the blocking rotor, and makes the flow path more stable with decreased points of fluctuation in flow from structural events. Therefore, it is desirable to maximize the efficiency of the blocking rotor by having only one cavity.
A third factor is that some displacement rotors are not balanced around their axis of rotation. This contributes to additional vibration and damage to the flowmeter. It is desirable to have balanced displacement rotors to minimize vibration.
All four of the sources described above, as well as others, contribute to the negative effects associated with increased flow rate such that a maximum useful flow rate is intrinsically imposed on the flowmeter simply by virtue of its design. These limitations within the current state of the art are founded on a series of technologies in the art beginning with George Richards' U.S. Pat. No. 2,835,229 in 1958.
The first embodiment of Richard's flow meter invention is the version built around a cylindrical blocking rotor with two recesses as show in FIGS. 1 through 10 of the 1958 patent. This version has been the model for most, if not all, of the flowmeters built since then within this type of flowmeter design. The design of the blocking rotor with two recesses used by Richards significantly obstructs the inlet and outlet ports, as evidenced by later patents, including Siebold's 1969 U.S. Pat. No. 3,457,835, Blomgren's 1969 U.S. Pat. No. 3,465,683 and Kolb's 1978 U.S. Pat. No. 4,109,525.
Additional attempts were made to try to remedy the problem of the blocking rotor. Kolb's 1996 U.S. Pat. No. 5,513,529 improves the design of the flowmeter by redirecting the inlet and outlet ports toward the displacement rotors and less toward the blocking rotors than in prior designs, but the historical trefoil configuration of the rotors still positions the blocking rotor to partially block the flow through the inlet and outlet, as seen in FIG. 1 of the Kolb 1996 patent.
Kolb's 1998 U.S. Pat. No. 5,808,196, made further modifications to the inlet and outlet ports, as well as an extension of the upper housing further down to shield the blocking rotor from direct inlet and outlet flow and to reduce vibrations. However, large turns in the flow path are still inherently required by the position of the blocking rotor relative to the inlet and outlet. Instead of the blocking rotor obstructing the flow path, that portion of the housing which shields the top of the blocking rotor now directly obstructs the inlet and outlet.
The Kolb 1998 patent also features a displacement rotor blade which during part of its rotation cycle, extends across the adjacent blocking rotor cavity almost to contact the central wall dividing the two blocking rotor cavities. In its rotation the displacement rotor blade must forcefully intrude, displacing and sweeping through the volume of fluid within the blocking rotor cavity. This action generates turbulence, uses increased energy and contributes to the pressure drop and to cyclical pressure drop fluctuations responsible for some of the remaining vibration in flow meters currently available in this design.
While attempts have been made to remedy the problem associated with the impact of the flow path and flow rate by the structure and components of the flowmeter, the use of a single cavity blocking rotor has not been used in the art. In Richards' 1958 patent, Richards uses a variety of algebraic formulas to describe the numerical relationships between the integral and geometric parameters shaping the elements in the various forms of his invention. These equations describe the angles between rotor axes and the angular extent of various arcuate surfaces all ultimately as function of two integral variables, B and D, where B is the number of recesses in the blocking rotor and D is the number of displacement rotors. Notably, Richards, as well as Kolb, all feature blocking rotors only with two or more recesses (B>=2). No one in the prior art has developed a single cavity blocking rotor (B=1) due to the fact that the prior art teaches away from a single cavity blocking rotor because the algebraic and geometric principles upon which the Richards and Kolb flowmeters were designed and configured preclude the very use of a single cavity blocking rotor.
In order to create a flowmeter with a single cavity blocking rotor, the long standing principles and formulas of Richards had to be contradicted for a new formula that incorporates structural changes to both the blocking rotor and the displacement rotors to permit a single cavity blocking rotor. The simpler and more efficient blocking rotor in the preferred embodiment is not possible applying Richards' principles and formulas.
In particular, Richards' principle (6) in his 1958 patent text column 9, lines 34-39 requires “the angular extent (β) of each sealing surface of the blocking rotor be equal to 360 degrees divided by the product of the number of recesses in the blocking rotor (B) and the number of displacement rotors (D).” Richards, and subsequent flowmeters modeled using his equations and principles, set (B) equal to or greater than 2. A double recess blocking rotor would require the angular extent (β) of the sealing surface on the blocking rotor to equal 360 degrees divided by 4, or 90 degrees. About 90 degrees is the largest blocking rotor sealing surface angular extent seen in the prior art.
Unlike any of Richards' embodiments' or any related prior art, the preferred embodiment of this new invention exhibits only one recess in the blocking rotor (B=1). Taking the single cavity blocking rotor (B=1) and two displacement rotors (D=2) and applying Richard's equations results in an angular extent (β) of the sealing surface on the blocking rotor to equal 360 degrees divided by 2, or 180 degrees, and the angular extent of the blocking rotor recess to also equal 180 degrees. Since these two angular components entirely describe the blocking rotor's circular cross-section, such a blocking rotor would render the flowmeter useless since it would fail to provide a continual sealing surface between the blocking rotor, the displacement rotors and the interior surface of the chamber, or else physically interfere with the displacement rotor blades.
In the preferred embodiment, the angular extent of the blocking rotor sealing surface is around 300 degrees with one recess, an embodiment that is not possible with Richards' principle (6). This new approach to flowmeter technology permits a unique blocking rotor and casing design that are far outside the parameters allowed by Richards' formula. Only by contradicting the longstanding principles and equations of Richards and the subsequent developed technology based upon his science is the single cavity blocking rotor possible.
Next, Richard's principle (8) (in his 1958 patent text column 9, lines 49-52) requires the angular extent (φ) of the surface on the casing making sealing contact with the blocking rotor to be >=Δ, in this case >=180 degrees. However, Principle (5) (in his 1958 patent text column 9, lines 34-40) requires the angle between the axes of the two displacement rotors to equal 360 degrees divided by the number of recesses (B) in the blocking rotor less the angular extent (β) of the sealing surface of the blocking rotor, or 360/1−180 degrees=180 degrees. Thus for this design configuration, Richards' principle (5) also places the axes of the two displacement rotors 180 degrees apart, requiring the displacement rotor hubs to meet the blocking rotor in exactly the same physical space in which the sealing surface of the casing also would meet the blocking rotor.
This would necessarily locate the physical material of the casing simultaneously in the same volume of space where the sealing surfaces of at least one displacement rotor hub must meet the sealing surface of the blocking rotor, a physical impossibility, which if it were somehow made possible—say with a casing of nearly zero thickness—would still fatally interfere with full rotation of the displacement rotor blades.
Under Richard's equations, designs with a single cavity blocking rotor and more than two displacement rotors (B=1 and D>2) fail for the same reason. Richards' equations result in unworkable interference between the casing and one or more of the displacement rotors in all such cases.
In the preferred embodiment the angle between the axes of the two displacement rotors is 180 degrees. However, choosing parameters far outside the bounds of Richards' principle (6) in the preferred embodiment, the angular extent of the blocking rotor sealing surfaces is about 300 degrees, much greater than the prescribed 180 degrees. This shrinks the angular extent of the blocking rotor recess down from 180 degrees to about 60 degrees instead. Correspondingly, the angular extent of the casing surface which seals with the blocking rotor then is also shrunk down to about 60 degrees, positioning said casing well outside of each displacement rotor blade's path of rotation.
FIGS. 6, 7, 8, and 9 show a range of designs where the angular extent of the blocking rotor sealing surfaces ranges between 210 and 300 degrees, illustrating alternative embodiments of this invention. These ranges are not to be construed as limiting. Angular value parameter choices anywhere within this continuous range, and somewhat beyond it at either end, are feasible under the new principles. This is unlike Richards' claims which specifically limit this angle to 360 degree/BD, where B and D must be small integers, i.e., B=the number of recesses in the blocking rotor and D=the number of displacement rotors.
Another key difference between more recent prior art blocking rotors and the preferred embodiment is that instead of Kolb's (1998 patent) circular end walls recessed into circular depressions machined into the housing end plates, the preferred blocking rotor end walls are circular minus just enough of a cutout to allow for cooperation between the rotation of the displacement rotor blades and the blocking rotor end wall without necessarily recessing the blocking rotor end wall into impressions in the end plate, simplifying their manufacture.
End wall to end wall, Kolb's blocking rotor is axially longer than his displacement rotors, while the preferred blocking rotors are the same length as the preferred displacement rotors. Circular end walls with a small cutout maintain most of the extra strength and rigidity provided by Kolb's light weight blocking rotor with end walls, while also allowing simpler flat end plates, i.e., no need to machine circular recessions/depressions for the blocking rotor, thus allowing each end plate to be simpler to manufacture by virtue of its working surface being flat in a single plane. The preferred embodiment still allows recessing the blocking rotor into the housing end plate if desired for other reasons.
Prior art used a 90 degree angle between the three rotor axes, necessarily positioning the blocking rotor so as to define and require a flow path in which the blocking rotor and/or the blocking rotor sealing surface of the casing is necessarily located where it must force sharp turns in the flow path at both the inlet and outlet and also directly obstructing flow and forcing a sharp turn below the blocking rotor, between the two displacement chambers, contributing to the pressure drop.
It is therefore desirable to have a flowmeter with a flow path that can accommodate an increased flow rate but has decreased pressure drop, cyclical pressure drop fluctuation and vibration.
It is further desirable to have a flowmeter that can maintain accuracy despite increased flow rates due to a smoother and more fluid flow path through the meter.
It is further desirable to have a flowmeter with a compact housing with in-line inlet and outlet ports for universal replacement of other compact in-line flowmeters of competing and less accurate varieties.
It is further desirable to have a flowmeter with easy in-line replacement installation in tight locations where flowmeters needing the added length of custom runners would be ruled out.
It is further desirable to have a flowmeter with high maximum flow rates exceeding similarly sized prior models.
It is further desirable to have a flowmeter with accuracy over a range of flow rates exceeding the current state of the art for positive displacement flowmeters.